Weapons can now be modified. Right-click a gun in your inventory and choose Modify to open its parts screen, which shows what is fitted, what it does to the weapon, and what you are carrying that would fit.
The first part is the Silencer. It turns up on better-equipped scavs and is not common.
You can also fit a part by dragging it straight onto the gun, either in your pack or in the weapon slot. And you can modify the gun you are currently carrying: right-click it in its weapon slot.
Removing a part gives you back that exact part, not a replacement.
The Silencer
A suppressed gun is dramatically quieter. Gunfire normally pulls zombies from a long way off; with a silencer fitted, only what is nearby reacts. It is the difference between clearing a building and being surrounded in it.
Suppressed weapons have their own firing sound.
Fitting one steadies the weapon a little and costs a little damage. It is a trade, not a straight upgrade.
A silencer needs a barrel built to take one. It fits most guns, but not shotguns, not the RPD, and not the scrap pistol - that one is welded together out of salvage and has nothing to thread onto.
A silenced gun is longer, and takes one more inventory cell.
Weapon appearance
Guns are now drawn assembled, with whatever is fitted to them, everywhere you see them: in your pack, in the weapon slots, while dragging, on the item info screen and on the mod screen. A suppressed rifle looks like a suppressed rifle.
Your equipped weapon shows its fitted parts on the weapon display as well.
Weapons being dragged are now drawn at the size they will actually take up, instead of being squashed into a square.
Fixes
A weapon whose size changes no longer jumps to a different spot in your pack. It grows where it sits.
Fitting a part is refused outright if the bigger weapon would have nowhere to go, rather than fitting it and leaving the gun stuck. The same goes for removing one when your pack is full - the part stays on the gun.